1. Field of the Invention
The present invention relates to a packaging process for a display device and, more particularly, to a packaging structure for an OLED/PLED device.
2. Description of the Related Art
In an organic electro-luminescence (EL) element used for new-generation panel display devices, such as organic light emitting diode (OLED) or polymer light emitting diode (PLED), electric current applied to specific organic luminescent materials transforms electricity into luminosity. The OLED/PLED device has the advantages of thin profile, light weight, high luminescent efficiency, and low driving voltage. However, as the duration of use increases, the likelihood of moisture and oxygen permeating the organic EL element also increases, causing detachment between the organic luminescent layer and the cathode electrode, cracking of the organic materials, and oxidation of the electrodes. As a result, a so-called xe2x80x98dark spotxe2x80x99, to which electricity is not supplied, is generated, decreasing luminescence and luminescent uniformity.
In order to prevent the internal space of the organic EL element from developing a high humidity condition, a sealing cap is commonly used to package the glass substrate on which metal electrodes and the organic luminescent layer are completed. Also, various technologies reducing the interior humidity have been developed, such as forming photo-hardened resin on the glass substrate, plating metal oxide, fluoride or sulfide on the glass substrate, forming a water-resistant film on the glass substrate, and using an airtight case to package the organic EL element. Nevertheless, other problems, such as leakage current, crosstalk and oxide dissolution, remain to be solved.
FIG. 1 is a sectional diagram showing a packaging structure for an OLED/PLED device according to the prior art. An organic EL element 10 comprises a glass substrate 12, a sealing agent 14 formed on the rim of the glass substrate 12, and a sealing cap 16 bonded to the glass substrate 12 by the sealing agent 14. Thus, the internal space 18 formed by the glass substrate 12 and the sealing cap 16 becomes an airtight container. Also, in the internal space 18, the glass substrate 12 comprises a lamination body 20 formed by a cathode layer 26, an organic luminescent material layer 24 and an anode layer 22. The sealing cap 16 of metal or glass is slightly smaller than the glass substrate 12 to cover the lamination body and reveal predetermined electrodes for driving circuits of the packaging structure.
The sealing agent 14 is polymer agent, such as UV-cured resin, epoxy resin and acrylic resin used in packaging LCD devices. With regard to organic luminescent materials sensitive to oxygen, moisture and high temperature, the polymer agent has poor resistance to moisture in the internal space 18 and poor adhesion between the glass substrate 12 and the sealing cap 16. The epoxy resin commonly used in the sealing agent 14 is a gather-type polymer and needs specific functional groups to carry polymerization out and thus space in position to the polymerization becomes a channel for moisture and oxygen. Also, during polymerization, vias and free volume are formed to become another channel for moisture and oxygen. Therefore, epoxy resin containing a large amount of moisture cannot provide good water/oxygen-resistance ability and easily allows the metal and organic luminescent material layer 24 to peel from the cathode layer 26.
Seeking to solve the problems caused by epoxy resin, a conventional method disposes a drying substance on the bottom of the sealing cap 16 and spaced from the lamination body 20 by an internal space 18 filled with dried inert gas. The drying substance comprises a solid compound, such as BaO, CaO, CaSO4, and CaCl2, which chemically absorbs moisture and maintains its solid state. When a large amount of BaO or CaO is added to the drying substance, the moisture absorbency of the drying substance is increased. Unfortunately, the moisture absorbency is limited when the thickness of the drying substance exceeds a critical value. Thus, a new method of packaging the organic EL element solving the aforementioned problems is called for.
The present invention provides a packaging structure for an OLED/PLED device, in which a sealing agent is an alloy with a low eutectic point to solve the conventional problems.
The packaging structure has a glass substrate on which a luminescent element is completed, and a sealing cap that is bonded to the rim of the glass substrate so as to seal the luminescent element within an airtight space. Also, a sealing agent is disposed between the rims of the sealing cap and the glass substrate, wherein the sealing agent is an alloy with a low eutectic point about 100xcx9c300xc2x0 C.
Accordingly, it is a principal object of the invention to provide an alloy with a low eutectic point as the sealing agent to provide good adhesion between the glass substrate and the sealing cap in a low melting temperature.
It is another object of the invention to provide the sealing agent without any channel for moisture and oxygen.
Yet another object of the invention is to provide the sealing agent with good resistance to the permeation of water and oxygen from the atmosphere.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.